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Extended-spectrum-β-lactamases (ESBLs)-producing Escherichia coliconferred resistance to most β-lactams, except for carbapenems. To date, the transmission mechanism of blaCTX-M, as the most common ESBLs subtype, in E. colihas received sustained attention around the worldwide, but the research on the pathogenicity of blaCTX-M-bearing E. coliis still scarce. The aims of this study were to discern the spread characteristics of ColV (encoding colicin V) plasmids in blaCTX-M-positive E. coli. The multi-drug resistance traits, phylogroups, and ColV plasmid profilings were screened in 76 blaCTX-M-positive E. coli. Thereafter, the genetic profiles of E. coliG12 and GZM7 were determined by whole genome sequencing, conjugation and S1-pulsed-field gel electrophoresis. The median lethal dose was analyzed in E. coliG12 and TG12A, the ColV-plasmid transconjugant of G12. Of all 76 blaCTX-M-bearing E. coli, 67.11% exhibited resistance to at least 2 drugs in addition to ceftiofur, 14.47% carried ColV-positive plasmids, and 53.95% were phylogroup C. Further studies demonstrated that the blaCTX-M-bearing E. coliG12 was assigned to the predominant lineage O78:H4-ST117 of phylogroup G. In addition, its ColV-positive plasmid simultaneously carried multiple resistance genes, and could be independently transferred to confer partial pathogenicity on its host by plasmid mating. E. coliGZM7 was O53:H9-ST23 of phylogroup C, which belonged to another representative lineage of APEC (avian pathogenic E. coli). Its ColV-positive plasmid could complete conjugation with the help of the other coexisting-resistance conjugative plasmid, although it failed to transfer alone. Our findings highlight the flexibly horizontal transfer of ColV plasmids along with multidrug-resistant genes among blaCTX-M-bearing E. coliposes a threat to poultry health and food safety, which contributes to elucidate the concept of “One Health” and deserves particular concern.

This study was designed to depict prevalence and antimicrobial resistance characteristics of Proteus mirabilis(P. mirabilis) strains in 4 chicken farms and to probe the transfer mechanism of resistance genes. A total of 187 P. mirabilisisolates were isolated from 4 chicken farms. The susceptibility testing of these isolates to 14 antimicrobials showed that the multidrug resistance (MDR) rate was as high as 100%. The β-lactamase resistance genes blaOXA-1, blaCTX-M-1G, blaCTX-M-9Gand colistin resistance gene mcr-1were highly carried in the P. mirabilisisolates. An MDR strain W47 was selected for whole genome sequencing (WGS) and conjugation experiment. The results showed that W47 carried 23 resistance genes and 64 virulence genes, and an SXT/R391 integrated conjugative elements (ICEs) named ICEPmiChn5 carrying 17 genes was identified in chromosome. ICEPmiChn5 was able to be excised from the chromosome of W47 forming a circular intermediate, but repeated conjugation experiments were unsuccessful. Among 187 P. mirabilisisolates, 144 (77.01%, 144/187) isolates carried ICEPmiChn5-like ICEs, suggesting that ICEs may be the major vector for the transmission of resistance genes among MDR chicken P. mirabilisstrains in this study. The findings were conducive to insight into the resistance mechanism of chicken P. mirabilisstrains and provide a theoretical basis for the use of antibiotics for the treatment of MDR P. mirabilisinfections in veterinary clinic.

This study was undertaken to discern the transmission characteristics of mcr-1and blaCTX-M-typein one multidrug-resistant Escherichia coliLWY24 from chicken in China. The genetic profiles of LWY24 isolate were determined by conjugation, S1-pulsed-field gel electrophoresis, southern blot hybridization and whole genome sequencing analysis. Meanwhile, co-transfer of plasmids in LWY24 isolate was screened by dual conjugation assays. The LWY24 isolate was identified as ST93, and harbored three conjugative plasmids, pLWY24J-3 (blaCTX-M-55-bearing IncFⅡ), pLWY24J-mcr-1(mcr-1-carrying IncI2) and pLWY24J-4 (non-resistance-conferring IncI1), and one non-conjugative plasmid pLWY24 (blaCTX-M-14-containing IncHI2/IncHI2A). Numerous resistance genes, insertion sequences (especially IS26), and transposons were found in the four plasmids, suggesting that horizontal transmission have occurred by plasmid mating, homologous recombination and transpositions. Under the selection pressure of cefotaxime and colistin or cefotaxime alone, the mcr-1-bearing plasmid and the blaCTX-M-55-harboring plasmid could be co-transferred at a similar frequency, with 8.00×10-4or 9.00×10-4transconjugants per donor cell, respectively. The specific shufflon region in mcr-1-encoding plasmid could generate up to six diverse PilV structures, which may further accelerate the horizontal transfer of plasmid. In conclusion, the transmission characteristics of mcr-1and blaCTX-M-typein LWY24 isolate could due to clonal spread of ST93, selective pressure of cefotaxime, IS26-mediate homologous recombination and transposition, and the specific shufflon region.

Here, the mechanisms of colistin heteroresistance (CHR) were assessed in 12 Escherichia coliisolates from swine in China. CHR was investigated by population analysis profile tests. CHR stability was studied by culturing isolates for five overnight incubation periods in colistin-free medium. Subsequently, the mcr-1gene and mutations in PmrAB, PhoPQ, and MgrB were screened in parental isolates and resistant subpopulations. Additionally, the expression levels of phoPQ, its target gene pagP, and its negative regulator gene mgrB, as well as pmrABand its target genes pmrHFIJKLMand pmrC, were determined by real-time relative quantitative PCR.